1. Field of the Invention
The present invention relates to a weldless joint for use in a process gas pipe system in a semiconductor manufacturing line.
2. Description of Related Art
In conventional semiconductor manufacturing lines, a process gas which possesses strong toxicity, e.g., silane gas, is used. Each of various devices connected to the semiconductor manufacturing line is generally retained and replaced so that the inside of the device is not exposed to air in order to prevent the deterioration of performance.
For example, a purge joint 100 shown in FIG. 9 has been provided in the semiconductor manufacturing line to substitute inert gas for the strong toxic process gas, thereby preventing the presence of the process gas at the time of replacement of the devices. Also, the devices are replaced so that the inside thereof is not exposed to air.
Such a purge joint 100 is explained with reference to FIGS. 9 and 10. FIG. 9(a) is a sectional exploded view of the purge joint 100 and FIG. 9(b) is a left side view of FIG. 9(a). FIG. 10 is a sectional exploded view of the purge joint 100.
The purge joint 100 is a weldless joint for connecting two pipes 112A and 112B as shown in FIG. 9. This purge joint 100 has a joint body 114 with six spanner holes 114d on the right end plane in the drawing. The pipe 112A is inserted into a cavity 114B of the joint body 114 through an opening formed in the right end plane of the body 114.
The pipe 112A is provided on its periphery with an annular groove in which an inner ferrule 116A having a wedge-shaped cross section is fitted. The inner ferrule 116A is provided with a plurality of cut-out grooves (not shown) formed in an axis direction so that it can be expanded to be slid onto the pipe 112A and mounted in place. These attached inner ferrule 116A can be moved integrally with the pipe 112A in an axial direction thereof.
An outer ferrule 115A is disposed on the right side of the inner ferrule 116A so that they are engaged with each other. A thrust bearing 120A is mounted on the pipe 112A on the right side of the outer ferrule 115A, whereby the pipe 112A does not rotate even if the joint body 114 is rotated.
The cavity 114b opens on the left end of the joint body 114 and is provided with a stepped large diameter portion having a female screw 114a. A nut member 113 having a male screw 113a formed on a periphery thereof is screwed into the female screw 114a. The nut member 113 is provided with a center hole in which the pipe 112B is inserted toward the cavity 114b. The nut member 113 also has on the left end thereof six spanner holes 113b.
Similarly, the pipe 112B is provided on its periphery with a pipe groove in which an inner ferrule 116B having a wedge-shaped cross section is fitted. The inner ferrule 116B is provided with a plurality of cut-out grooves (not shown) formed in an axis direction so that it can be expanded to be slid onto the pipe and attached in place. The so attached inner ferrule 116B can be moved integrally with the pipe 112B in an axial direction of the pipe.
An outer ferrule 115B is disposed on the right side of the inner ferrule 116B so that they are engaged with each other. A thrust bearing 120B is mounted on the pipe 112B on the right side of the outer ferrule 115B, whereby the pipe 112B does not rotate even if the joint body 114 is rotated.
The left end plane of the outer ferrule 115B is in contact with the right end plane of the nut member 113. A gasket 119 provided with a center hole is attached to the tip end of the pipe 112B. The gasket 119 is made of soft metal and is sandwiched under pressure between the pipes 112A and 112B, thereby serving as a seal which prevents gas leakage from the contact surfaces of the pipes 112A and 112B.
An outer port 114C is formed in the joint body 114 at a position corresponding to the connecting area of the pipes 112A and 112B and the clearance forming area between the pipes. This outer port 114C communicates with a port 118a of an outer joint 118 having a male screw on the periphery thereof.
The process for connecting the pipes 112A and 112B using the purge joint 100 shown in FIG. 9 is explained. The pipes 112A and 112B in a separated state are shown in FIG. 10 and will be connected in a manner that the nut member 113 is screwed into the joint body 114 as the pipes 112A and 112B make contact with each other through the gasket 119. It is to be noted that the screwing of the nut member 113 into the joint body 114 is made with a spanner through the spanner holes 113b and 114d.
As the nut member 113 is screwed into the joint body 114, the outer ferrule 115B is pushed rightward in the drawing, which pushes the inner ferrule 116B rightward, and further the pipe 112B rightward. Accordingly, the pipe 112B is made to press the pipe 112A through the gasket 119. At this time, the thrust bearing 120B allows the pipe 112B to move without rotating even when the nut member 113 being rotated presses the outer ferrule 115B.
On the other hand, the pipe 112A presses the inner ferrule 116A rightward via the pipe groove. The pressing force of the inner ferrule 116A is exerted on the joint body 114 through the outer ferrule 115A. As mentioned above, the thrust bearing 120A allows the pipe 112A to move without rotating even when the outer ferrule 115A presses upon the joint body 114.
Accordingly, when the nut member 113 is screwed into the joint body 114, the pipes 112A and 112B compress the gasket 119 therebetween whereby to seal the contact surfaces of the pipes. At this time, the area where the pipes 112A and 112B are in contact, namely, the location of the gasket 119 is always in a predetermined position. The opening 114C is formed corresponding to this position.
If the nut member 113 is loosened on the joint body 114, a clearance between the pipes 112A and 112B is produced in an area corresponding to the opening 114C. In this state, evacuation and purge processes are repeated to substitute inert gas for process gas in the pipes 112A and 112B. Thus, the purge joint 100 utilizes the outer joint 118 as a purge port.
Subsequently, if the nut member 113 is screwed into the joint body 114 to connect the pipes 112A and 112B, no air enters in the pipes 112A and 112B. The devices connected to the pipes 112A and 112B can be replaced with different devices without the inside of the devices being exposed to air.
However, the purge joint 100 is provided with an O-ring 117, which is fitted to the nut member 113, to prevent air from entering in the cavity 114b. Because the O-ring 117 is disposed between the nut member 113 and the joint body 114 high torque is required for the screwing of the nut member 113 into the joint body 114.